Reinforced composite structures, such as rotor blades for wind turbines, can be produced by means of a process known as VARTM (Vacuum Assisted Resin Transfer Molding). In such a process, which is e.g. described in WO 2009/103736 A2, resin and hardener is mixed in a mixer which in turn supplies the mixed resin to the mold. The flow of the mixed resin to the mold is driven by vacuum in the material to be casted and is, depending on the size of the mold, provided through one or more mold inlets. The mixer is normally only capable of supplying the mixed resin within a certain flow range. Furthermore, the needed flow for the cast may vary over time during the casting process. Therefore, the mixed resin is supplied via a buffering container which can compensate for this difference between supply and need. However, such a buffering container may release unhealthy vapors to the environment or even accidentally be tipped-over. Accordingly, the buffering container has a negative influence on the working environment.
When using the above described VARTM process, it is difficult to control the propagation of resin in the laminate. This is due to the fact that areas with a relatively high concentration of fiber material constitute a higher flow-resistance than areas with a relatively low concentration of fiber material.
EP 1 859 920 B1 describes how the above problem can be reduced by adding distribution layers to the material which is to be casted. Such distribution layers make it possible for the resin to easier propagate to other areas of the structure. However, the distribution layers do not contribute to the strength of the casted structure after curing. Further, if the distribution layers are removed from the cured structure, they leave a negative impression on the surface of the structure, such that additional post-treatment is required to re-establish the desired surface form.
A further problem of the VARTM process is that static pressure drops may occur between mold inlets which are arranged at different heights. Such pressure differences will cause different amounts of resin to flow through the mold inlets per time unit.
There may be a need for an improved and simple way of casting composite structures.